FIG. 1 shows a configuration disclosed in Patent Literature 1 as a conventional example of a connector-incorporating plug 10 of this type. FIG. 1 illustrates a barrel 11 and a coupling 12. The barrel 11 having a tube shape includes a built-in optical connector, although it is hidden in FIG. 1. The coupling 12 is mounted to the outer circumference of the barrel 11 at its front end so as to be movable along the center axis of the barrel 11.
This connector-incorporating plug 10 is of a push-pull connection type. It can be connected to a mating receptacle by grabbing the barrel 11 and pushing it in a single operation, and can also be extracted from the mating receptacle by grabbing the coupling 12 and pulling it backwards in a single operation.
In order to be able to visually check that the coupling goes forward to a predetermined position to make the connector-incorporating plug 10 connect to the mating receptacle, a groove 13 appearing when the coupling 12 goes forward to the predetermined position is formed as a mark on the outer circumference of the barrel 11.
Patent Literature 2 also mentions that a groove appearing when a coupling goes forward to a predetermined position is formed on the outer circumference of a barrel and that it is checked by looking at the groove that the connector-incorporating plug is appropriately connected to a mating receptacle.